Guralp Systems Scream - Manual (Page 83)

User guide
Usually, the values of the STA and LTA periods, and of the Ratio, will
be the same for all ticked channels. For convenience, Scream! will
automatically fill in other values to match ones you enter. If you want
to use different values for some channels, you should clear the
Common values check-box before altering them.
Once you have enabled the STA/LTA triggering method on a particular
channel, you can use the Control window to change the values of the
STA and LTA periods, together with the Ratio, without restarting the
digitiser (see Chapter 8 on page 89).
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